1. Field of the Invention
The present invention relates to a tape cartridge having a front lid for protecting tape, and more specifically to an improved lock means for holding the front lid in a closed position.
2. Description of the Prior Art
Generally in a tape cartridge there is provided a lock means inside the case body of the tape cartridge so as to lock a front lid in a closed position in order to prevent the front lid from opening and the tape from being damaged when operating the tape cartridge.
As shown in FIG. 1, in a known cartridge there is provided a lock means 15 formed of an elongated plate spring (resilient) member in which the rear end portion is fixed to the inner surface of the rear portion of the side wall 24 of the cartridge case and there is defined a lock tip 16 for detachably engaging an engaging recess 23 defined in an inner surface of an edge portion of a front lid 10. A release button 17 projects from the middle portion of the lock means 15 through a window of the side wall 24 from the inside to the outside of the case and 3 upon depressing the release button 17 from the outside to the inside, the front end portion of the lock means 15 is resiliently biased away from the side wall 24 of the case so as to release the engagement between the lock tip 16 and the engaging recess 23.
In the conventional lock means 15 the plate spring member including the plate portion of the lock means are resiliently biased, whereby the lock tip 16 is detachably engaged with the engaging recess 23 defined in the front lid 10. Moreover, in order to obtain a predetermined spring characteristic, the lock means 15 is held in a cantilevered manner by being fixed to the rear portion of the side wall 24 of the case body 1 so that the bending, oscillating span of the lock plate means is made larger. Therefore, the intermediate portion of the lock means 15 lies in the most adjacent portion between a tape reel 3 and the side wall 24 of the case. Therefore, there is the disadvantage that the lock means 15 may contact the tape 4 and damage it when operating the release button 17.
In order to avoid such a problem, the thickness of the side wall 24 of the conventional cartridge case has been made thin so that the lock means 15 is separated from the tape reel 3 as far as possible. However, it is still insufficient to prevent the abutting disturbance between the lock means 15 and the tape 4. On the contrary, the thinning of the side wall 24 of the case body 1 results in a lock of strength of the cartridge case. Therefore, there occurs a new problem that the case body 1 is easily deformed torsionally only by applying a small force or that the side wall 24 will break or be damaged when the case is, for example, dropped.
Moreover, since the engagement state between the lock top 16 and the engaging recess 23 is maintained only by the elastic force of the lock means 15, which is in a free condition, it is difficult to obtain a sufficient engagement force for locking the front lid 10. Therefore, there has been the fear that the front lid 10 may be opened by applying a small external force. Furthermore, since the lock means 15 is made of a plastic molded resin, when using the tape cartridge in a high temperature, there occurs creep deformation in the lock means 15 so that there is a chance of further lowering the engagement force of the lock means 15 and therefore a problem regarding the reliability thereof.